1. Technical Field
The present invention relates to a gas pressure-driven type pretensioner for an automobile seat belt, in which a gas generator and a gas pipe are joined or fastened together by crimping an end-adjacent portion of the gas pipe onto the gas generator, and a production method therefor.
2. Description of the Related Art
Generally, an automobile is equipped with a seat belt system for restraining and protecting an occupant by a seat belt, in the event of a collision or a sudden stop of the automobile. In the seat belt system, the seat belt is received in a winder or retractor during non-use, and then withdrawn from the retractor before use. In a normal state, the seat belt can be freely withdrawn from the retractor during use of the seat belt system. Further, if slack occurs in the seat belt, the seat belt is automatically wound up by the retractor until the slack is removed. Thus, even though the seat belt, which is withdrawn from the retractor and in contact with an occupant, is kept in a tightened state without slack, it never hinders an occupant's movement for driving.
In the event of a collision or a sudden stop of the automobile, in response to a sudden force applied to the seat belt in a direction causing withdrawal of the seat belt from the retractor, the seat belt is locked within the retractor, so that it is kept from being further withdrawn from the retractor. This makes it possible to restrain an occupant to a seat so as to prevent forward movement of the occupant.
However, in the event of a collision or a sudden stop of the automobile, the operation of locking the seat belt involves a slight response lag or time delay. Consequently, the seat belt will be withdrawn from the retractor excessively to some extent. Moreover, depending on a posture or a seated position of an occupant, there is a possibility that the seat belt is in a position where it is slightly excessively withdrawn from the retractor, in the normal state.
In the event of a collision or a sudden stop of the automobile, if the seat belt is in such a position where it is slightly excessively withdrawn from the retractor, the seat belt system cannot adequately fulfill an occupant restraining or protecting function. Therefore, a seat belt system has been employed which is additionally provided with a pretensioner designed to wind up a seat belt or pull a seat belt in a direction for increasing a restraining force thereof, almost instantaneously in the event of a collision or a sudden stop of an automobile, to enhance the occupant restraining or protecting function. As one type of pretensioner, there has been known a gas pressure-driven type pretensioner using a gas generator adapted to generate a high-pressure gas based on combustion of a gas-generating agent, as a power source for winding up or pulling a seat belt (see, for example, JP 2000-326824A).
As one example of the gas pressure-driven type, a pretensioner can be employed which comprises a gas generator adapted to generate a gas when a shock is applied to an automobile due to a collision or a sudden stop thereof, and a gas pipe adapted to guide the generated gas to a piston, wherein a seat belt is wound up or pulled by means of movement of the piston. Generally, in the conventional gas pressure-driven type pretensioner, the gas generator is placed within the gas pipe made of a metal, at a position on the side of one end of the gas pipe. Then, the gas generator and the gas pipe are joined or fastened together by crimping the end portion of the gas pipe onto the gas generator.
FIG. 7 shows one example of a joined portion between a gas generator and a gas pipe of a conventional gas pressure-driven type pretensioner. For example, in this conventional pretensioner, the gas generator 101 and the gas pipe 102 are joined or fastened together in the following manner. Firstly, the gas generator 101 is placed in a hollow portion inside the gas pipe 102 made of a metal, at a position on the side of one end of the gas pipe 102. Then, an end-adjacent portion 103 of the gas pipe 102 is crimped onto a crimping shoulder 104 of the gas generator 101, so that the gas generator 101 and the gas pipe 102 are joined or fastened together.